It is known that containers, such as bottles or cans, can be provided with an imprint for identification of the container content, where the printing ink is at a printing station by use of a direct printing head applied directly onto the container. The containers are for this purpose transported in the container handling machine by use of a transport device and the direct printing heads print onto them in a two-dimensional manner. Such a direct printing head is, for example, an inkjet printing head comprising a plurality of typically vertically arranged nozzles (for example, 500-1000). A rotational motion of the container about its longitudinal axis and/or a pivotal motion of the printing head is typically performed for two-dimensional printing. The printed image itself is available as digital information in a computer controller and is used for respective actuation of the direct printing head, the container receptacles and/or a pivot unit. Furthermore, the printing ink is in a subsequent curing device curved with UV or electron beams by cross linking. Several printing units with different printing inks (printing colors) are provided for multi-color printing. It is with such direct printing methods possible to provide the container with an individual print.
The drawback here is that the fine nozzles of the direct printing heads can occasionally clog with printing color and/or contaminants, where already a single clogged nozzle causes a significant error in the print result. Furthermore, it is possible that scattered radiation of the curing device unintentionally cures excess ink on the direct printing head.
To this end, DE 10 2009 058219 A1 suggests that direct printing heads be cleaned by using a cleaning device in regular cycles. The printing head to be cleaned is there in a cleaning position mechanically dabbed off by a dabbing device and/or excess printing ink is removed by an extraction device.
The disadvantage here is that highly dried or partially cured ink residues must be removed with a respectively strong mechanical action of the dabbing device and the nozzles can thereby be damaged. Furthermore, particles can also be introduced by the dabbing device into the non-clogged nozzles and clog them.
It is furthermore known from DE 10 2006 052154 A1 that printing ink is for cleaning purposes jetted from the ink-jet printing head so as to flush the nozzle from the inside.
A disadvantage is that a relatively large amount of printing ink is consumed by this cleaning process and the distribution of the ink used as cleaning fluid is not uniform at the printing head. Furthermore, highly dried or cured ink residue on the printing head can with this method be difficult to remove.